Synergetic Effect of Facet Junction and Specific Facet Activation of ZnFe₂O₄ Nanoparticles on Photocatalytic Activity Improvement

Abstract

Crystal facet engineering has been proved as a versatile approach in modulating the photocatalytic activity of semiconductors. However, the facet-dependent properties and underlying mechanisms of spinel ZnFe₂O₄ in photocatalysis still have rarely been explored. Herein, ZnFe₂O₄ nanoparticles with different {001} and {111} facets exposed were successfully synthesized via a facile hydrothermal method. Facet-dependent photocatalytic degradation performance toward gaseous toluene under visible light irradiation was observed, where truncated octahedral ZnFe₂O₄ (ZFO(T)) nanoparticles with both {001} and {111} facets exposed exhibited a superior performance than the others. The formed surface facet junction between {010} and {100} facets was responsible for the improved activity by separating photogenerated e^-/h⁺ pairs efficiently to reduce their recombination rate. Photogenerated electrons and holes were demonstrated to be immigrated onto {001} and {111} facets, separately. Intriguingly, electron paramagnetic resonance trapping results indicated that both ^•O₂^- and ^•OH were abundantly present in the ZFO(T) sample under visible light irradiation as major reactive oxygen species involved in the photocatalytic degradation process. Additionally, further investigation revealed that {001} facets played a predominant role in activating photogenerated transient species H₂O₂ into ^•OH, beneficially boosting the intrinsic photocatalytic activity. This work has not only presented a promising strategy in regulating photocatalytic performance through the synergetic effect of facet junction and specific facet activation but also broadened the application of facet engineering with multiple effects simultaneously cooperating.